The present invention relates to a DC to AC converter. More particularly, the invention relates to a converter for converting power from a DC source to AC power with controlled voltage and frequency. The converter of the invention may also convert AC power at one voltage and frequency to AC power at a different voltage and frequency.
For AC to AC conversion, the incoming AC power is first converted to DC by a rectifier and filter capacitor. The basic system operates from DC.
There are four principal parts to the known converter. A rectifier/capacitor is provided for operation from AC power. An oscillator or signal generator is utilized to generate the required output waveform. A DC to DC converter having tightly controlled positive and negative outputs is provided. The output voltages of the DC to DC converter vary in accordance with signals derived from the oscillator or signal generator. A linear amplifier is also utilized. The linear amplifier has positive and negative input voltages supplied by the DC to DC converter and controlled directly by the oscillator or signal generator.
In the DC to DC converter of the prior art, the DC input power is converted to positive and negative DC supplies with voltages greater than the peak values of the AC output. These supplies power a conventional linear or audio amplifier. While the system is simple it is not very efficient. The maximum possible efficiency occurs when the peak output voltage equals the relevant supply voltage, and is theoretically 78.5%, ignoring drive losses. In practice, the maximum achievable efficiency is less than 70%, and consequently the overall efficiency of the supply, including losses in the DC to DC converter, is typically between 50% and 60%.
The principal object of the invention is to provide a DC to AC converter having a high overall efficiency.
An object of the invention is to provide a DC to AC converter which produces a high quality output waveform.
Another object of the invention is to provide a DC to AC converter which supplies just enough voltage across the linear amplifier for satisfactory operation.
Still another object of the invention is to provide a DC to AC converter providing optimum efficiency by adjusting the positive and negative supply voltages to be as close as possible to the peak output without incurring amplifier distortion.
Yet another object of the invention is to provide a DC to AC converter wherein the positive and negative supply voltages are made to follow the AC output voltage as closely as possible, at all times, thereby optimizing the overall efficiency.
Another object of the invention is to provide a DC to AC converter having an amplifier efficiency of greater than 78.5%.
Still another object of the invention is to provide a DC to AC converter having an overall efficiency greater than 60%.